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Wednesday, January 20, 2010

Things to love about Australia: Meteorological Phenomena

A story about something unusual I witnessed on my trip to Australia in November 2008:

I had flown to Alice Springs to join a three day tour of the most famous sites in the Central Desert. One of the things I was especially looking forward to was stargazing since this was going to be the furthest I'd been from anywhere (no light pollution). Also, we would be sleeping outside at campsites.

My hopes of stargazing were let down during our first night at Yulara. Not only was there a full moon, but the 41°C (106°F) day became a cloudy evening. However... I got to see something much rarer than a clear sky of stars. At 3:30 am, I was woken up by a light fall of rain as drops landed on my face. I knew it was 3:30 am because the full moon reflected so much light off the clouds that it was bright enough outside to read my watch. It was still very hot so the raindrops dried as soon as they fell.

As I was lying there on top of my sleeping bag in the rain, looking up at the bright moon and illuminated clouds, I saw an arch of light in the sky. It looked like a greyscale rainbow. It was the strangest thing. Have you ever seen a rainbow in the dark? I had never thought about it before. I kept looking at the band of light but it faded away by the time the other campers woke up.

I forgot about the arch of light until a few weeks later when it occurred to me to do a web search on nighttime rainbows. It turns out that what I had seen was a moonbow, also known as a lunar rainbow! The principle is the same as a rainbow, but because moonlight is weaker than sunlight, the full spectrum of colours can't usually be seen by the human eye. A certain set of conditions must be in place for a moonbow to be visible: "The Moon must be less than 42 degrees high in the sky, the sky must be very dark and there must be rain falling opposite the Moon. Moonbows are more common near waterfalls." In my situation, the sky wasn't dark, but there was only moonlight, no artificial light. Also, I was in the middle of the desert, nowhere near a waterfall, so I feel like seeing a moonbow there is even more unusual.

I believe I'm very lucky to have seen a rare and special lunar rainbow.